A color filter used in a color liquid crystal display, which is currently extremely widespread, is configured so that colored pixel layers R, G, and B (respectively corresponding to red, green, and blue) are formed on a transparent substrate, and that a black matrix is formed on each of the gaps between adjacent ones of the colored pixels R, G, and B so as to enhance display contrast. Especially, in a liquid crystal display device of the active matrix driving type using TFTs, the black matrix is used to prevent picture quality from being degraded due to an electric current leakage caused by irradiating light onto the TFTs. In recent years, a high optical density (O.D.), which is equal to or higher than 4.0, has been demanded for the black matrix so as to enhance the display contrast of a displayed image. On the other hand, the surface smoothness of the color filter is reduced by increasing the thickness of the black matrix. Thus, it is necessary that the black matrix is formed like a thin film.
Hitherto, a metallic thin film has been used to manufacture a black matrix for a display device, which has a high light shieldability. The black matrix is manufactured by performing the following method (see “Color TFT Liquid Crystal Display”, published by Kyoritsu Shuppan Co., Ltd., Apr. 10, 1997, pp. 218 to 220.). That is, a photoresist is applied onto a metallic thin film made of a metal such as chrome, which is formed by performing an evaporation process or a sputtering process. Subsequently, the photoresist is exposed and developed using a photomask having a light shielding film pattern for a display device. Then, the exposed metallic thin film is etched. Finally, the photoresist remaining on the metallic thin film is peeled and removed to form the black matrix.
This method uses a metallic thin film. Thus, even in a case where the thickness of the film is small, a high light shielding effect is obtained. However, this method requires a vacuum film formation step of performing the evaporation process or the sputtering process, and also requires an etching step. Thus, this method has a problem in that the cost of the black matrix is high. Additionally, because the metallic film is used, the reflectance of the film is extremely high. Thus, this method has another problem in that the display contrast is low under strong external light. On the other hand, a method using a low reflectance chrome film (including, for example, two layers respectively made of metallic chrome and chromic oxide) has been proposed. However, because waste liquid containing metallic ions is discharged in the etching step, this method has a major problem in that an environmental load is large. Especially, chrome, which is most frequently used, is harmful and has a very large environmental load. Recently, as implied by EU directives such as ELV and RoHS, there has been increased public concern about reduction in the environment load. A metal material to be substituted for chrome has been proposed.
Meanwhile, one of techniques of obtaining a black matrix, whose environment load is small, is a technique using carbon black (see, for example, JP-A-62-9301 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). According to this technique, as shown in FIG. 7, a photosensitive resin composition containing carbon black is applied onto a substrate 1. This applied layer is dried. Then, a black matrix BM is obtained by exposing and developing the dried layer. However, the optical density of a unit application amount of carbon black is low. Thus, to obtain a high light-shieldability and a high optical density, the thickness t of the film is necessarily increased.
In the case of using carbon black, when an optical density of, for example, 4.0, which is equivalent to that of the metallic film, is ensured, the thickness of the film should be 1.2 μm to 1.5 μm. Therefore, in a case where RGB pixels are formed after the black matrix BM is formed, sometimes, boundary parts of adjacent colored pixels R and G expand as projected portions 3, 3, for example, as shown in FIG. 7. In a color filter 5 the planarity and smoothness of which are impaired, external light passes through the projected portion 3 around the black matrix and causes leakage of light from a thin film transistor (TFT) due to irradiation of light thereonto. Consequently, the technique using carbon black has problems in that picture quality is degraded, and that light from a backlight light source is incident from a side part of the projected portion 3 to thereby degrade display quality.
A method using metal microparticles instead of carbon black is known as a method of obtaining a black matrix that has a small environment load and a high optical density and that is formed as a thin film, in view of the above problems (see, for example, JP-A-2004-240039). According to this method, a black matrix, which has a small environment load and a high optical density and which is formed as a thin film, can be obtained, as compared with the method of forming a metallic thin film.
In the case of a black-matrix-equipped filter formed using metal microparticles, the film thickness of the black matrix can be reduced, as compared with the case of forming a black matrix using carbon black. Also, in the case of a filter with a black matrix formed using metal microparticles, the environment load can be reduced, as compared the case of forming a black matrix using a metal thin film.